Footwear, footwear inserts and socks for reducing contact forces

ABSTRACT

Footwear, footwear inserts and socks that include a cavity adapted to receive a portion of an individual&#39;s heel foot to reduce contact forces. The cavity can be adapted to contain a liquid, a solid or two layers of material in which the stiffness of the layers differ.

BACKGROUND OF THE INVENTION

The present invention generally relates to footwear, footwear insertsand socks for reducing contact forces on an individual's body.

Many physical activities involve repeated impacts between anindividual's feet and the ground surface. For example, during a fivekilometer run an individual's body experiences approximately 3,000impacts with the ground. These impacts generate forces on the bodycommonly known as peak forces within the first ten to thirtymilliseconds of a foot coming into contact with the ground surface. Aforce-time wave (also known as an impact shock wave) is generated eachtime an individual's foot makes impact with the ground surface.Unfortunately, immediately after an impact shock wave is created it doesnot remain contained within the individual's foot but rather traversesthrough the knee and hip joints toward the individual's brain.

A shock wave can be characterized by its amplitude or peak force (A) andduration (T) with both of these parameters depending upon severalfactors such as the speed at which the individual is running, the natureof the ground surface upon which the individual is running (for example,soft versus hard), the anatomy of the foot, and the runner's runningstyle. Moreover, these parameters depend upon whether the individual iswearing footwear, footwear inserts and/or socks as well as the materialand design of the footwear, footwear inserts and/or socks. Of the twoparameters, A and T, if A (the force amplitude) is of a sufficientmagnitude, then it can cause both short and long term detrimentaleffects on an individual's body. For example, it can cause one or moreof the following: (i) damage to the soft tissue structures within theknee and hip joints, (ii) low back pain by enhancing forces on thelumbar spine, and (iii) stress fractures when the body is burdened withexcessive physical exercise over a very short period. Measurements haveshown that the shock wave amplitude A during casual running can exceedten to twenty times the runner's bodyweight. Moreover, these highforces, which are a result of the downward momentum (or velocity) of anindividual's body that is brought to virtually zero immediately after anindividual's foot contacts the ground, are dynamic in nature and lastfor only ten to thirty milliseconds. This is analogous to the situationin which a fast-moving baseball caught by a catcher produces a forceseveral times in magnitude the baseball's weight. Thus, footwear,footwear inserts and socks that minimize the amplitude (A) of a shockwave could help minimize detrimental impact-related effects on anindividual's body.

For day-to-day activities such as normal walking and stair climbing theforces within the knee and hip joints can easily reach five times theforce of an individual's bodyweight. This somewhat counterintuitiveresult occurs because an individual's joint counterbalances the tensileaction of the muscles acting on the joint by undergoing compressionitself so as to satisfy force equilibrium conditions. Since on anaverage an individual walks about five kilometers a day this translatesinto approximately 1.2×10⁶ heel strikes with the ground surface for eachfoot per year. The long-term effects of the impact pulses generated witheach heel strike on the soft tissue structures of the knee and hipjoints has been well established. The cumulative effect of the impactpulses is to cause joint arthritis. The time to develop this conditiondepends upon the type and frequency of the physical activity such aswalking, running or playing sports.

The amplitude A is roughly the velocity V at which the foot strikes theground (considering only its vertical component) divided by the time ittakes the ground to bring the downward velocity of the body and henceits momentum to zero (known as the ground interaction time T). Since thespeed at which a person's feet strike the ground is usually set by therunner and therefore “non-negotiable” one way to reduce A is to increaseT. This can be accomplished by running on grassy and softer surfaces, orequivalently, by avoiding runs on hard pavements. Another way toincrease T, which has been widely exploited heretofore by the footwearindustry, is to provide an easily deformable thick rubber sole at theheel portion of the shoe. During each heel strike, the rubber sole makescontact with the ground first and then it compresses continuously underthe action of the downward moving heel while providing an increasinglyupward resisting pressure to the heel of the foot. This resistingpressure acts to reduce the downward velocity of the heel and actsduring the entire time that the sole material is being compressed. Oncethe sole material underneath the heel has been fully compressed whilethe heel does feel the impact from the ground below the magnitude ofthis impact is now significantly reduced as the heel strikes the groundwith a much lower velocity due to the upwardly directed pressure fromthe deforming sole. Viewed alternatively, the time taken by the solematerial to compress increases the overall time T for bringing the heelvelocity to zero. This strategy to reduce impact force amplitude byincreasing T is identical to that employed by a baseball catcher whilecatching a fast pitch. By moving his catching hand in the same directionas the arriving baseball, the impact on his hand is considerablydecreased. This is because this action of moving the catching handincreases the time T over which the velocity of the arriving baseball isbrought to zero.

When applied to footwear, there are practical limitations to decreasingthe force amplitude A by arbitrarily increasing the time T for exampleby providing a very soft sole material in the heel section of the shoe.This is because if the material is too soft (e.g., a soft foam), it willsimply deform without providing the necessary resisting pressure to slowdown the downward (towards the ground) velocity of the striking heel.Therefore, the heel will essentially suffer the same impact with orwithout the sole material. Moreover, at another extreme the materialunderneath the heel cannot be too hard either as higher stiffness tendsto increase A. Various manufacturers and designers have focused ondifferent structural and material strategies to provide the optimalstiffness (not too soft and not too hard as discussed above) in the heelsection of the shoe for reducing A. Some of these strategies include useof novel polymers with optimal levels of stiffness, incorporation of airpockets within the heel section of the sole material, and the additionof plastic protrusions or patterns of small structural units in the formof beams and columns in the heel section of the shoe's sole. In thelatter strategy, the amplitude of the shock wave A is reduced byincreasing the time T for arresting the upper body momentum throughdeflection and bending of the beam and column network. There have alsobeen suggestions to design soles using active materials whose stiffnesscan be changed depending upon the ground stiffness, much like thedynamic suspension system used in many modern cars. Regardless of thesophistication of the material or the mechanical technology used, thefact remains that each one of the prior art focuses on providing someform of padding material directly between the striking heel and theground surface.

As can be seen, there is a need for footwear, footwear inserts and socksthat can lower impact forces inside the knee and hip joints. Inaddition, there is a need for footwear, footwear inserts and socks thatcan lower the shock wave amplitude inside the knee and hip joints. Also,there is a need for footwear, footwear inserts and socks that manage andmitigate the physical effects on an individual's body caused by groundimpact forces.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, footwear for mitigatingimpact forces on an individual's heel bone includes an outsole unithaving an outsole upper side and an insole unit having a insole lowerside secured to the outsole upper side and an insole upper sideincluding a cavity wherein the cavity is adapted to receive the heelbone portion (including the soft-tissue that covers the heel bone) of anindividual's foot.

In another embodiment a footwear insert for mitigating impact forces onan individual's heel bone includes an insole unit adapted to be insertedinto footwear including a cavity wherein the cavity is adapted toreceive the heel bone portion of an individual's foot.

In yet another embodiment a sock for mitigating impact forces on anindividual's heel bone includes a cavity adapted to receive the heelbone portion of an individual's foot.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an article of footwear for mitigating impactforces on an individual's heel bone in which the article of footwear hasan insole unit that includes a cavity to receive the heel portion of anindividual's foot according to one embodiment of the present invention;

FIG. 2 is a side view of an article of footwear for mitigating impactforces on an individual's heel bone having an insole unit that includesa cavity to receive the heel bone portion of an individual's footaccording to one embodiment of the present invention;

FIG. 3 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit having an outsole upper side and an insole unit having ainsole lower side secured to the outsole upper side and an insole upperside including a cavity wherein the cavity is adapted to receive theheel bone portion of an individual's foot according to one embodiment ofthe present invention;

FIG. 4 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit having an outsole upper side and an insole unit having ainsole lower side secured to the outsole upper side and an insole upperside including a cavity containing a substance (such as a solid, aliquid and/or a gas) wherein the cavity is adapted to receive the heelbone portion of an individual's foot according to one embodiment of thepresent invention;

FIG. 5 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit having an outsole upper side and an insole unit having ainsole lower side secured to the outsole upper side and an insole upperside including a cavity containing a first layer and a second layerwherein the first layer is disposed above the second layer and the firstlayer does not have the same level of stiffness as does the secondlayer, in which the cavity is adapted to receive the heel portion of anindividual's foot according to one embodiment of the present invention;

FIG. 6 is an elevation view of a footwear insert for mitigating impactforces on an individual's heel bone including an insole unit adapted tobe inserted into footwear in which the insole includes a cavity whereinthe cavity is adapted to receive the heel bone portion of anindividual's foot according to one embodiment of the present invention;

FIG. 7 is an elevation view of a footwear insert for mitigating impactforces on an individual's heel bone including an insole unit adapted tobe inserted into footwear in which the footwear insert includes a cavitythat is filled with a substance (such as a solid, a liquid and/or a gas)or substances (such as a first layer and a second layer wherein thefirst layer is disposed above the second layer and the first layer doesnot have the same level of stiffness as does the second layer) accordingto one embodiment of the present invention; and

FIG. 8 is a side view of a sock for mitigating impact forces on anindividual's foot having an insole unit that includes a cavity toreceive the heel portion of an individual's foot according to oneembodiment of the present invention.

INTELLECTUAL FRAMEWORK FOR THE CLAIMED INVENTION

The intellectual framework for the claimed invention in this applicationis based on a study in which knee forces were measured in professionaland casual runners. This study is discussed to provide the scientificbasis for the claimed invention. This study researched the impact shockwaves (both A and T) experienced by various runners. In this study,instead of directly measuring A, the acceleration-time wave wasmeasured, which is exactly proportional to the impact shock wave andcharacterized by an amplitude B and the same time T as that of theimpact shock wave. The impact shock wave's amplitude A can be obtainedby multiplying the acceleration wave amplitude B by the mass of therunner. Use of acceleration pulses in the study therefore allowedcomparing shock wave amplitudes for runners with different weights(masses). Accordingly, the amplitude of the impact shock wave A ismeasured in units of lb-f or Newton, while B is measured in units ofacceleration, ft/s² or m/s². Moreover, sometimes the amplitude B isconveniently expressed in units of g, which is the acceleration due togravity. When B is set to equal 1 g, this results in a shock waveamplitude A equal to one times the runner's bodyweight, which isessentially the force experienced by the body when the runner isessentially standing. Accordingly, 5 g will produce shock wave amplitudeA that is 5 times the runner's bodyweight. The value of B when expressedin terms of g thus provides a very convenient way to compare intensitiesof forces in terms of runner's bodyweight. For this reason B is alsoreferred to as the “G-Force,” in the biomechanics community.

Since impact shock is known to vary systematically with running speedand surface gradient (Clarke, T. E., Cooper, L. B., Clark, D. E., &Hamill, C. L., 1985, “The effect of increased running speed upon peakshank deceleration during ground contact.” In D. Winter, R. Normal, R.Wells, K. Hayes, & A. Patla (Eds.), Biomechanics, IX-B, pp. 101-105,Champaign, Ill.: Human Kinetics and Hamill, C. L., Clarke, T. E.,Frederick, E. C., Goodyear, L. J., & Howley, E. T., 1984, “Effects ofgrade running on kinematics and impact force.” Medicine and Science inSports and Exercise, 16, 185), changing the speed and gradient of amotorized treadmill provides a convenient means of manipulating thelevels of impact shock in a laboratory environment. In the research,each subject walked and ran on a motorized treadmill (Precor956) at 1.3m·s⁻¹ (3 mph; average walking speed), 2.8 m·s⁻¹ (6.3 mph), 3.3 m·s⁻¹(7.4 mph), 4.2 m·s⁻¹ (9.4 mph) and 5.0 m·s⁻¹ (11.2 mph). Subjects wereallowed to rest between trials. The use of treadmill allowed maintaininga proper control over walking and running speeds across differentrunners.

Subjects were selected from a pool of volunteers to participate in theseexperiments. The selection was based on running experience in whichprofessional athletes were chosen which run a minimum 50 km and casualrunners were chosen which run at least one time a month. Moreover, allrunners were chosen with the same shoe size (U.S. size 11). However, theweights and heights of the runners were however allowed to vary in thestudy. This control, as discussed below, allowed for a betterunderstanding of the mechanism of dramatically reducing shock wavesreduction in professional athletes compared with casual runners.

Regarding the instrumentation of the research, skin-mountedaccelerometers have been used before to measure the shock wavestransmitted into the body during running. Following this approach, axialaccelerations of the lower right leg were recorded in various runners bymeans of a piezo-resistive accelerometer (PCB Model 3701D1FB20G)attached to the skin onto the anterior-medial (front and center) portionof the tibia (shin bone) just distal (just below the knee level) to theknee joint. The sensitive axis of the accelerometer was aligned with thelong axis of the bone. This site was selected because the soft tissueoverlying the bone is relatively thin at this point and this minimizesthe signals resulting from the muscle action, which in turn was oflittle interest to this study. To facilitate the attachment, theaccelerometer was bonded inside a wooden mounting block. The block washeld in position by a Velcro strap and tightened to the comfort level ofthe runner. Such tightening has also been shown to reduce the influenceof soft tissue on the accelerometer signal. While the accelerometeritself has a mass of 77.8 g and a nominal resonant frequency superior to900 Hz, the mass of the encased accelerometer was 83 g with its naturalfrequency inclusive of its attachment is between 60 Hz and 90 Hz. Whilethe dominant component in the acquired acceleration signal relates tothe impact shock wave, it also includes components corresponding tomuscular action and noise resulting from the compliant attachment of theaccelerometer to the body. Spectral analysis was used to distinguish andseparate the impact shock wave data from these unwanted signals. Outputsfrom the accelerometer were sampled using an oscilloscope (Tektronics,MSO4000 Series) and processed using a computer using software (Wavestarfor Oscilloscopes). Each sample taken contained at least 3 correct peaksof acceleration before it was considered for analysis.

The results indicate that professional long distance runners take theimpact on their forefoot by maintaining smaller steps and pushing higherwhile a casual runner runs with longer strides that results in takingthe impact on his or her heels. At 7.4 mph running speed, peakaccelerations in the range of 4 g to 5 g (which corresponds to a dynamicforce 4 to 5 times the body weight) were recorded in causal runners justbelow their knees while they ranged between 2 g and 3 g for aprofessional athlete. Both sets of runners wore the same-size shoes fromthe same top of the line brand. The reduction in G force in aprofessional athlete substantially cuts down the impact on his knee andhip joints. However, this reduced G-force comes at the expense of highlystraining his Achilles' tendon that undergoes substantial tension toreduce the forefoot impact force. Moreover, over a long distance run theprofessional runner can in fact fatigue his Achilles' tendon.Interestingly, the results have indicated that use of shoes that arewell padded towards the heel (that is, with thicker soles) can destroyprofessional athlete's years of hard work by increasing his or herG-force to the same level as experienced by a casual runner. That is,when the same professional athlete was given a high performance shoethat had a fairly thick sole in the heel region of his shoes his G-forcewas significantly higher compared with when he or she ran bare feet orwith shoes with very thin heels. A thicker sole automatically results ina heel strike with the ground surface first even for a professionalathlete. This happens naturally because of the thick-soled geometry ofthe shoe. This hypothesis is supported by the data shown in Table 1 ofFIG. 9A, which shows the G forces measured in a professional runner withtwo different shoe designs. Shoe A had a much thicker sole in its heelregion compared with that in Shoe B.

Based on the above discussion, one can conclude that whenever a person'sheel strikes the ground first during running it generates substantiallyhigher force amplitudes compared to when the impact is taken first bythe forefoot. When the heel portion of the shoe strikes the groundfirst, the reaction force from the ground is almost immediately directedin line with the axis of the shinbone. The shock wave thus created islaunched immediately into the shaft of the shinbone towards the kneejoint and the only attenuation (reduction in the shock wave amplitude)it receives is caused by the soft tissue structure that is directlycovering the heel bone. In addition to the direction, the entire forceis generated over a very small area of the heel bone, which results in avery large contact pressure (force divided by contact area). The largecontact pressure very quickly compresses both the natural tissueoverlaying the heel bone and the sole material of the shoe that isdirectly underneath the heel area. This then leads to a much shortertime T and an increase in the shockwave amplitude A, as discussed above.

In considering the situation for a professional athlete running barefoot that results in a minimum value of the shock wave or accelerationpulse amplitude, the impact generates a shock wave however it isdirected to an area forward of the ankle joint. The generated shock wavetravels to the ankle first, and then turns almost 90 degrees into theshaft of the shinbone to proceed towards the knee joint. It is wellknown in the field of shock wave physics field that there is asignificant dissipation in the amplitude of the shock wave when it turnsby a significant angle, as here, by almost 90 degrees into the shaft ofthe shinbone. This natural turning of the shockwave results in shockwave attenuation not present in ordinary runners where the wave isgenerated directly in line with the shaft of the shinbone. Even moreimportant than this effect is a second effect resulting from footrotation about the ankle joint that occurs immediately after impact. Thefoot essentially acts like a rotational spring and increases the time Tover which the upper body momentum is brought to zero upon foot impact.Any increase in T, as discussed above, will bring down the amplitude ofthe shock wave A. The same foot rotation mechanism also works for “flatfooted runners,” such as marathoners, who do not experience forefootimpact that would significantly fatigue their Achilles tendons.Moreover, the area of contact upon the impact is much larger in theforefoot-impacted region because there are no protrusions of any kindunderneath the forefoot in contrast to the downwardly protruding apex ofthe heel bone in the heel region. This effect is even larger for flatfooted runners. A large area reduces the impact pressure (force per unitarea) and thus it takes more time to compress the material of the sole.The synergistic effect of all these mechanisms leads to this dramaticdecrease in the impact shock wave amplitude in a professional athletecompared with that experienced by a casual runner. One can also see whythis beneficial effect disappears as soon as the professional athleteruns with shoes with a thicker sole in the heel region that results inthe impact point and hence the center of pressure essentially movingtowards the heel region. Indeed, the results have shown that one of theprofessional athletes running at 7.4 mph, 9.4 mph and 11.2 mphexperienced G forces of 4.6 g, 4.5 g and 4.5 g, respectively, whichcompares well with the corresponding figures of 4.5 g, 5.0 g, and 5.5 grecorded for a casual runner at the same speeds. The same professionalathlete recorded 3.6 g, 3.4 g and 3.8 g, respectively, at the abovespeeds, when using a shoe which had a very thin sole in its heel regionand therefore the athlete was still able to strike his forefoot firstwithout the geometry of the shoe forcing him to land on his heels first.One can therefore conclude that a professional athlete should avoidwearing thick heel shoes during running.

The claimed invention in this application are a result of the naturalquery as to which design for shoes, shoe inserts and socks could becreated for a casual runner that will yield the reduced G-forces forcesobtained by a professional runner achieve through years of training! Theclaimed invention as well as actual force measurements using the claimedinvention are discussed next.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Referring now to the figures, FIG. 1 is a top view of an article offootwear 10 for mitigating impact forces on an individual's foot andconsequently to his or her body in which the article of footwear 10 hasan insole unit 15 that includes a cavity 17 to receive the heel portionof an individual's foot according to one embodiment of the presentinvention. While in one embodiment of the present invention the cavity17 extends through part of the thickness/depth of the insole unit inanother embodiment of the present invention the cavity extendsthroughout the whole thickness/depth of the insole unit. In oneembodiment of the claimed invention there is absolutely no supportprovided directly underneath the heel bone (also known as calcaneus) ofa person's foot but rather upward resisting pressure or support to thedownward moving heel is provided annularly around the heel bone, whichdramatically cuts down the force amplitude on the heel bone. Thisreduces the overall force of the foot and to the body.

The following is a list of different types of footwear according toindividual embodiments of the present invention, which is not meant tobe exhaustive: athletic shoes, tennis shoes, cleats, climbing shoes,hiking shoes, skating shoes, cycling shoes, skateboarding shoes, golfshoes, snow shoes, wrestling shoes, ski boots, work shoes, dress shoes,boots, sandals, flip flops, mules, pumps, high heels, slingbacks,esparilles, clogs, platform shoes, mocassins, loafers, boat shoes,slippers, dance shoes, bowling shoes, childrens' shoes and correctiveshoes.

While insole unit 15 can include any type of material, preferably it ismade of a cushioning material that includes a synthetic foam such aspolyurethane, polyolefin, or the like according to one embodiment of thepresent invention. Insole unit 15 can function alone according to oneembodiment of the present invention or in combination with otherfunctional units in an article of footwear 10 according to oneembodiment of the present invention.

FIG. 2 is a side view of an article of footwear 10 for mitigating impactforces on an individual's heel bone having an insole unit that includesa cavity 17 to receive the heel bone portion of an individual's footaccording to one embodiment of the present invention. While as shown inthis embodiment of the present invention, the footwear 10 includes anoutsole unit 12 having an outsole upper side and an insole unit 15having a insole lower side secured to the outsole upper side and aninsole upper side including a cavity 17 wherein the cavity 17 is adaptedto receive the heel portion of an individual's foot, in anotherembodiment of the present invention the insole unit and outsole unit areconfigured as a unitary structure. While in this embodiment of thepresent invention the cavity 17 extends through part of thedepth/thickness of the insole unit 15 in another embodiment it extendsthe whole depth/thickness of the insole unit 15. Moreover, where insoleunit 15 and outsole unit 12 are configured as a unitary structure in oneembodiment of the present invention the cavity 17 extends through partof the depth/thickness of the unitary structure and in anotherembodiment of the present invention it extends through the whole of thedepth/thickness of the unitary structure. In one embodiment of theclaimed invention, the cavity 17 is filled with a substance (such as apolymer) that has a much lower stiffness coefficient value compared toeither the material that is used to make the rest of the insole unit 15(on which the foot rests inside the shoe) or to the material of theouter sole unit 12 (part of shoe that contacts the ground) of the shoe.

FIG. 3 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit 12 having an outsole upper side and an insole unit 15having an insole lower side secured to the outsole upper side and aninsole upper side that includes a cavity 17 wherein the cavity isconfigured to receive the heel bone portion of an individual's footaccording to one embodiment of the present invention. According to oneembodiment of the claimed invention the heel bone (including the softtissue that covers it) 35 of a person's foot 30 is received into thecavity 17 and the foot is supported by the insole unit 15 to therebymitigate any impact forces on the heel bone portion 35. In otherspecific embodiments of the claimed invention, the cavity 17 can bedesigned to have a different shape and/or tailored to meet differentshapes and sizes of types of footwear and of the specific needs ofindividual's feet.

In one embodiment of the claimed invention a cavity is incorporateddirectly in the construction of the footwear or sock itself where apartial cavity will be placed in the heel area of insole of the footwearor sock. Even though the invention has been demonstrated with a specificcavity or cutout diameter and depth, they can all be varied to any sizedepending upon the weight and foot anatomy of the user. The design couldalso be introduced in a customized manner in which an individual's footanatomy could be scanned to produce a shoe that maximizes the scientificeffect of the claimed invention. Moreover, the cavity could be designedto be adjustable in one embodiment of the claimed invention.

FIG. 4 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit 12 having an outsole upper side and an insole unit 15having a insole lower side secured to the outsole upper side and aninsole upper side including a cavity 17 configured to contain asubstance 40 (such as a solid, a liquid and/or a gas) wherein the cavity17 is configured to receive the heel bone portion of an individual'sfoot according to one embodiment of the present invention. According toone embodiment of the claimed invention the heel bone portion 35 of aperson's foot 30 is received into the cavity 17 and the foot 30 issupported by the insole unit 15 and the heel bone 35 is supported by asubstance 40 (such as a solid, a liquid and/or a gas) to therebymitigate any impact forces on the heel bone portion 35. In otherspecific embodiments of the claimed invention, the cavity 17 can bedesigned to have a different shape and/or tailored to meet differentshapes and sizes of types of footwear and of the specific needs ofindividual's feet. In one embodiment of the claimed invention, duringthe initial stages of person's foot 30 striking the insole unit 15, asthe heel bone portion 35 drives into the cavity 15 as it compresses thesubstance 40 and the substance 40 in turn begins to support the heelbone portion 35 due to the increase in stiffness of the substance 40caused by the downward-moving heel bone portion 35, which extends thetime T over which the support to the heel bone is provided resulting ina reduction of the force amplitude A.

In one embodiment of the claimed invention a cavity is incorporateddirectly in the construction of the footwear, footwear insole or sockitself in which a partial or full cavity is placed in the heel area ofinsole of the footwear, footwear insole or sock. In one embodiment ofthe claimed invention the aforesaid cavity is filled partially orcompletely with a substance such as a polymer that is much softer (orhas a much lower stiffness coefficient value) compared with the materialthat is used to make the shoe's insole or its outer sole. During theinitial stages of the heel strike, this idea works identically to thefirst one where the support to the heel bone is provided annularly bythe stiffer material present at the edges of the soft polymer-filledcavity and the forefoot. However, as the heel drives further into thecavity by compressing the soft polymer, the soft polymer starts tosupport the heel bone as well as its own stiffness increases uponcompression caused by the downward-moving heel. This extends the time Tover which the support to the heel bone is provided which in turnreduces the force amplitude A. Experiments were done with this designfor casual runners and the results showed that the level of low G-forcesrecorded earlier using an unfilled cavity were essentially reproduced,and in some cases, even superior results were obtained as shown in Table2 of FIG. 9B. Even though this concept was demonstrated with onespecific polymer that filled the cavity, any material that has anelastic stiffness lower than the surrounding insole material or thematerial used to form the outer sole of the shoe should result inreduced impact forces. One advantage of this embodiment is that it alsoprovides a good feel to the user and be likely preferred over the firstembodiment. Table 2 of FIG. 9B shows data for a casual runner.Interestingly, since the professional runner uses forefoot impact(discussed later in the application), the filling of the hole with apolymer that is located in the heel section of the shoes did not provideany beneficial effects as shown in Table 3 of FIG. 9C.

In another embodiment of the claimed invention, the cavity is filledwith a number of widely available cooling gels, medicated pads or evenaromatic gels for those suffering from foul foot odor. This mayparticularly prove attractive to patients suffering from diabetics andother foot diseases.

In one embodiment of the claimed invention there is a cutout or a cavityin the heel region of the shoe's insole directly underneath where theapex of the heel bone and its soft tissue covering (or the protrudingportion of the heel bone) contacts the shoe's insole during normalwalking and running. In principle the diameter of the cutout should beslightly larger than the footprint of the heel bone (without the softtissue) on the shoe's insole. The depth of the cutout is such thatbefore the apex of the heel bone gets to the bottom of the cavity andthe ground reaction starts to build up directly underneath it, the areaof the heel immediately surrounding the heel bone apex contacts theareas of the insole, at and immediately, adjoining the edges of thecavity. This latter contact occurs as the apex of the heel bone isstilling moving (downwards) unsupported inside the cavity. The pressurefrom the ground reaction builds up immediately on the annular portionsof the heel, around the apex of the heel bone, since those areas comeinto contact with the edges of the cavity first. This resisting pressuresubstantially decelerates the apex of the heel bone that is still movingdownwards towards the ground but has not yet contacted the bottom of thecavity. Interesting during this time while the heel bone is still movingdownward without experiencing any direct upward resistance from theground, the forefoot region of the foot impacts the ground through thesole. At this point both the annular area around the apex of the heelbone and certain areas of the forefoot start to compress the portions ofthe sole directly beneath them. All this happens while the apex of theheel bone has not contacted the ground yet. The resisting pressure atthese areas results in further reduction of the speed by which the apexof the heel bone is approaching the ground. Finally, at some point, theapex of the heel bone contacts the bottom of the cavity and thisimmediately results in additional resistance from the ground because ofthe compression of the sole that is now directly underneath the apex ofthe heel bone. This resisting pressure is added onto the alreadyoperating resisting pressure that continues to act over the forefoot andannular area of the heel surrounding the apex of the heel bone. Thecombined effect of this is that the center of reaction-pressure on theheel is now shifted away from the heel bone apex towards the front ofthe foot. As discussed above, this immediately brings into action thebeneficial effects of foot rotation about the ankle joint, additionalshock wave attenuation due to wave bending at the ankle joint, and anincrease in T caused by a reduction in the contact foot pressure. Fromthe viewpoint of impact shock wave management, this effectively convertsa casual runner who is a heel striker to a forefoot professional runneror even a flat foot marathon runner. This fact was established bymeasuring the impact shock wave amplitude A just below the knee level inboth casual as well as professional runners all of whom wore the samesize and brand-named shoes in which a cavity slightly larger than theapex of the heel bone was provided in the heel region of the shoes'insoles. The depth of the cavity varied between 5 mm and 10 mm over theheel area, with the smallest depth towards the forefoot. Experimentswere also done using a thicker insole in which the depth of the cavityvaried between 10 mm and 20 mm over the span of the heel region. Resultsfor casual runners showed that the shock wave amplitude could be reducedby 20% by using shoes in which holes or cavity were provided in the heelregion of the insoles. Results for one of the professional runnersshowed that the use of the claimed invention reduced the G force from1.5 g to 1.1 g at 7.4 mph, from 2.5 g to 2.2 g at 9.4 mph and 3.5 g to 3g at 11.2 mph. These represent reductions in the G-force ranging from12% to 25%, using the claimed invention. The reduced levels of G forceis even better than values of 1.0 g, 2.5 g and 3.5 g that were recordedduring bare feet running, which typically resulted in the lowest levelsof G force for the professional athlete. This essentially means that aprofessional athlete can better his impact management by using theclaimed invention. What is even more exciting is that this reduction inthe G-force level comes while also reducing the tension on his Achillestendon. This happens because the annular area of the athlete's heelaround the apex of the heel bone is fully supported and this takes offthe reactionary tension from his Achilles tendon. This means that aprofessional runner when using the technology disclosed in this patentmay be doubly benefited, thereby minimizing the impacts on his kneeswhile reducing the fatigue on his Achilles tendon. This can turn out tobe the difference between winning and loosing in a very competitiverace. The exact depth of the cavity that will maximize the beneficialeffects of the invention will depend upon the weight and foot anatomy ofthe runner and the specific material used for making the insole.

FIG. 5 is a cross-sectional view of a portion of FIG. 1 showing anoutsole unit 12 having an outsole upper side and an insole unit 15having a insole lower side secured to the outsole upper side and aninsole upper side including a cavity 17 configured to contain a firstlayer 50 and a second layer 55 wherein the first layer 50 is disposedabove the second layer 55 and the first layer 50 is stiffer than thesecond layer 55 wherein the cavity 17 is configured to receive the heelbone portion 25 of an individual's foot 30 according to one embodimentof the present invention. According to one embodiment of the claimedinvention the heel bone portion 35 of a person's foot 30 is receivedinto the cavity 17 and the foot 30 is supported by the insole unit 15and any impact forces on the heel bone portion 35 are distributed acrossthe area of the first layer 50 and will compress the second layer 55because the first layer 50 is stiffer than the second layer 55. In oneembodiment of the present invention, the first layer 50 has a stiffnesscoefficient value that is at least twice the stiffness coefficient valueof the second layer 55. In other specific embodiments of the claimedinvention, the cavity 17 can be designed to have a different shapeand/or tailored to meet different shapes and sizes of types of footwearand of the specific needs of individual's feet. In an other specificembodiment of the claimed invention, the first layer 50 and/or thesecond layer 55 comprises a two-phase composite material, with polymermatrix and a second material dispersed with a stiff phase such as in theform of a particle or fiber, for example.

FIG. 6 is an elevation view of a footwear insert for mitigating impactforces on an individual's heel and foot including an insole unit 65adapted to be inserted into footwear in which the insole includes acavity 67 wherein the cavity 67 is adapted to receive the heel boneportion of an individual's foot according to one embodiment of thepresent invention. In specific embodiments of the claimed invention, thefootwear insert can be configured to have different shapes, sizes and toaccommodate different shapes, sizes and types of footwear and to meetthe needs of individuals' different sized and shaped feet. While in oneembodiment of the present invention the cavity 17 extends through partof the thickness/depth of the insole unit in another embodiment of thepresent invention the cavity extends throughout the wholethickness/depth of the insole unit. According to one embodiment of theclaimed invention the heel bone portion of a person's foot is receivedinto the cavity 77 and the individual's foot is supported by the insoleunit 65 to thereby mitigate any impact forces on the heel and the footand consequently to the rest of the body.

In one embodiment of the claimed invention a removable footwear insertincludes a cavity in the heel area of the footwear insert, which it wasfound through testing to reduce the impact force between 20% and 44%.Motivated by this embodiment, tests were made of shoe inserts widelymarketed in world commerce today and compared them with ones similar tothe embodiment shown in FIG. 6 by placing them in athletic as well asformal leather shoes and comparing them to shoes without insoles.Moreover, the experiments were done with the same runners and shoes toallow for the quantitative study of the performance of the claimedinvention in managing shock waves that occur during normal walking andrunning. The results are summarized in Tables 1-3 of FIG. 9D. In Tables1-3 of FIG. 9D Shoe 1 refers to a shoe having no shoe insert; Shoe 2 isa shoe in which a top brand named shoe insert was placed, and Shoe 3contained a shoe insert as depicted in FIG. 6. The results showed thatirrespective of the type of runner, whether causal or professional, theresults summarized in Tables 1-3 of FIG. 9D show that the shoe insertsas depicted in FIG. 6 outperformed the other shoes in the study. Theresults indicate that the embodiment as depicted in FIG. 6 reduced thecontact force between 20% and 44%. This is an amazing decrease and asdiscussed later would dramatically increase the life of the cartilageand significantly delay the onset of arthritis.

Measurements were also made of the G-forces during normal walking andsince a large population goes to work in formal dress shoes, experimentswere extended to include these types of shoes as well. All measurementswere made at walking speed of 3 mph. Results for one of the femalesubjects showed that the G-force was 0.7 g when using no footwearinserts, 0.5 g when using a regular brand-named shoe insert, and only0.3 g when using the same footwear insert but with a hole provided inits heel area. The G-forces for other subjects did not show anyvariation as the natural padding of the athletic footwear provided theG-force decrement. Results using formal leather footwear showed benefitsto all users. For one of the subjects, the G-forces were 1 g when usingno footwear insert, 0.95 g when using a standard footwear insert, and0.8 g when using the footwear insert as shown in FIG. 6. Two additionalsubjects recorded values of 0.55 g, 0.65 g and 0.55 g; and 0.8 g, 1.gand 0.7 g, when using shoes with no footwear insert, a standard footwearinsert, and a footwear insert as shown in FIG. 6. This means that theuse of standard footwear inserts worsened the G-force for these tworunners. The claimed invention shown in FIG. 6 however restored theirG-forces, again showing the advantages of the claimed invention. Insummary, the above results indicate that the embodiment of the claimedinvention shown in FIG. 6 can reduce the G-force for normal walkingwhether using athletic or formal footwear by 12% to 20%. For someindividuals, no benefit was recorded but it never made it worst. Thisfinding could be significant for those who undertake work-relatedwalking and standing for prolonged periods of time such as assemblyworkers, railroad yard workers, postman, police officers, hospitalstaff, and firefighters.

FIG. 7 is an elevation view of a footwear insert for mitigating impactforces on an individual's heel bone including an insole unit 75 adaptedto be inserted into footwear in which the footwear insert includes acavity 77 that is filled with a substance 79 (such as a solid, a liquidand/or a gas) or substances (such as a first layer and a second layerwherein the first layer is disposed above the second layer and the firstlayer is stiffer than the second layer) according to one embodiment ofthe present invention. While in one embodiment of the present inventionthe cavity 17 extends through part of the thickness/depth of the insoleunit 75 in another embodiment of the present invention the cavityextends throughout the whole thickness/depth of the insole unit 75.According to one embodiment of the claimed invention the heel bone of aperson's foot is received into the cavity 77 and the individual's footis supported by the insole unit 75 and the individual's heel bone issupported by the substance 79 (such as a solid, a liquid and/or a gas)or substances (such as a first layer and a second layer wherein thefirst layer is disposed above the second layer and the first layer isstiffer than the second layer) to thereby mitigate any impact forces onthe heel bone.

FIG. 8 is a side view of a sock 87 for mitigating impact forces on anindividual's heel and foot having an insole unit 85 that includes acavity 89 to receive the heel bone portion of an individual's footaccording to one embodiment of the present invention. While in oneembodiment of the present invention the cavity 17 extends through partof the thickness/depth of the insole unit 75 in another embodiment ofthe present invention the cavity extends throughout the wholethickness/depth of the insole unit 75. According to one embodiment ofthe claimed invention the heel bone of a person's foot is received intothe cavity 77 in which the cavity contains a substance (such as a solid,a liquid and/or a gas) or substances (such as a first layer and a secondlayer wherein the first layer is disposed above the second layer and thefirst layer is stiffer than the second layer) whereby the individual'sfoot is supported by the insole unit 75 and the individual's heel boneis supported by the substance 79 (such as a solid, a liquid and/or agas) or substances (such as a first layer and a second layer wherein thefirst layer is disposed above the second layer and the first layer isstiffer than the second layer) to thereby mitigate any impact forces onthe heel and the foot.

The following is a list of different types of socks according toindividual embodiments of the present invention, which is not meant tobe exhaustive: athletic socks, hiking socks, ski socks, anklet socks,dress socks, medical socks and hosiery.

Even though embodiments of the claimed invention have been shown with aspecific diameter and cavity depth (or substance-filled areas), they canall be varied to any size depending upon chosen criteria such as theweight and foot anatomy of the user. The claimed design could beintroduced in a customized manner in which an individual's foot anatomycould be scanned to produce footwear or footwear inserts that maximizeimpact management. Along the same idea, prefabricated footwear orfootwear inserts that are size-dependent and age-dependent could bedispensed for example at the office of a Podiatrist, Orthopedist,Pediatrician, Chiropractor, etc., as the need may be determined.

Use of some of the particular embodiments of the claimed invention cutsdown the impact force amplitudes experience during normal walking orrunning anywhere from 20% to 30% over the heel technology utilized inthe most expensive top brand shoes being marketed today.

According to certain specific embodiments of the claimed invention, shoefootwear, footwear inserts and/or socks including a cavity are used forhigh heeled footwear. Prior research has shown that a person wearinghigh heeled footwear experiences not one but two shock waves. The twoshock waves occur almost next to each other in time. This is because theheel impacts the ground first and it is immediately followed by theimpact on the toe-region of the high heeled footwear. Both impactsresult in shock wave amplitudes that are similar to those discussedearlier in this application. Because of this, a person wearing highheeled footwear is essentially doubling the number of shock waves thatimpacts his or her body compared to when the person walks the samedistance using standard footwear. The basic invention that is discussedin this application can be used to reduce the two shock waves peaks toonly one and therefore significantly improve the detrimental effects onthe body of the wearer. For this purpose, a cavity in the heel sectionof the high heeled footwear is provided and/or in the footwear insertsor socks. The cavity is contoured so as to take the shape of the arch ofthe foot, meaning that the area in the heel section will be indenteddeeper compared to the inclined section of the high heeled footwearwhere the forefoot makes the contact. The depth and contour of thecavity can be customized for each individual, if needed. As the pointedportion of the heel strikes the ground the heel of the wearer will bestill moving downwards in the cavity so no reaction force or the impactshock wave will be generated. When the wearer's heel will strike thebottom of the cavity, the forefoot region will also strike the inclinedportion of the high heel shoes. The depth of the cavity is so designedthat the wearer's forefoot and heel will make contact with theirrespective supporting portions of the insole in the footwear, footwearinsert or sock almost about the same time. It is not necessary to makethe two contacts occur at exactly the same time but they must be closeenough. This will not only lead to one shock wave impact but itsmagnitude will also diminish significantly as it will bring into effectall the beneficial effects of forefoot walking as already discussedearlier in this application.

In addition to the shock wave management, there are added benefits ofspecific embodiments of the claimed invention. For example, the cavityin the footwear, footwear inserts and/or socks can also providestability to the foot with respect to pronation and suplination forindividuals engaged in sports such as tennis, squash, basketball and thelike where frequent and sudden movements are made by an athlete.Pronation refers to an inward roll of the foot during normal motion andoccurs as the outer edge of the heal strikes the ground and the footrolls inward and flattens out. When excessive pronation occurs the footarch flattens out and stretches the muscles, tendons and ligamentsunderneath the foot to cause injury. Suplination is the opposite ofpronation and refers to the outward roll of the foot during normalmotion and occurs during the toe push off portion of the gait. Excessivesuplination (outward rolling) places a large strain on the muscles andtendons that stabilize the ankle, and can lead to the ankle rollingcompletely over, resulting in an ankle sprain or total ligament rupture.

To fully appreciate the benefits of the claimed invention over prior artand to motivate the general population to embrace the claimedtechnology, a detailed discussion on its effect on increasing the lifeof bone cartilage and consequently delaying the onset of osteoarthritisin the joints is provided below. Specifically, the question that isanswered below is how significant medically is the effect of reducingthe G-forces by 10% to 30% as realized by the claimed invention over thepresently available footwear, footwear insert and sock technology.

The soft tissue structures comprising the joints undergo tribologicalwear and tear upon repeated interactions with the acceleration pulses.With time, depending upon an individual's level of physical activity,these joints become arthritic, a condition where the soft tissue padding(also called the cartilages on the articulating bones within the jointis mostly worn out such that during, weight-bearing gait phase, a directcontact between the ends of the articulating bones ensues. The loadsproduced by repeated impacts have also been linked to degenerative jointdiseases and athletic overuse injuries including stress fractures(Milgrom et al., “A Prospective Study of the Effects of aShock-absorbing Orthodic Device on the Incidence of Stress Fractures inMilitary Recruits”, Foot and Ankle, 1985, Vol. 6, pages 101-104), shinsplints (Detmer, “Chronic Shin Splints Classification and Management ofMedical Tibial Stress Syndrome”, Sports Medicine, 1986, Vol. 3, pages436-446), cartilage breakdown, and low back pain (Voloshin & Wosk, “Anin vivo study of low back pain and shock absorption in human locomotorsystem”, Journal of Biomechanics, 1982, vol. 5, pages 267-272).Interestingly, some studies have also suggested that repeated impactsincrease the rate of red blood cell breakdown and contribute to thedepressed iron status of many distance runners (Falsetti, Burke, Feld,Frederick, & Ratering, “Hermatological variations after endurancerunning with hard and soft-holded running shoes,” Physician and SportsMedicine, 1983, vol. 11(8), pages 118-127; Miller, Pate, & Burgess,“Foot impact force and intravascular hemolysis during distance running,”International J. Sports Medicine, 1988, vol. 9, pages 56-60). Eventhough the exact mechanisms of these injuries are still underinvestigation, there is no question that any effort to minimize theamplitude A of the shock wave can not only avoid short-term overloadinjuries but also significantly prolong the onset of degenerativediseases such as arthritis. How the amplitude A affects the latter hasbeen researched by Weightman (“Tensile Fatigue of Human Cartilage”, J.Biomechanics, 1976, vol. 9(4), pages 193-200) who performed cyclicfatigue experiments in-vitro (tested outside the body) on cartilagespecimens extracted from human cadavers of different ages. The extractedcartilages were loaded into a tension machine by straining the specimenfrom a zero stress (or Force) to a peak stress S (proportional toamplitude A, discussed here) and then the specimen was unloaded slowlyto zero stress. This constituted one loading cycle. The machine wasprogrammed to load the specimen with a large number of continuouscycles, each with an amplitude S. The number of loading cycles N thatcaused failure (fracture, damage, etc) of the cartilage was recorded.Their data is represented by the following empirical equation:

S=23−0.41a−1.83 log₁₀ N,  (1)

where S is the failure stress measured in units of MN/m², a is the ageof individual in years, and N is the number of cycles to failure, eachwith a maximum amplitude S. In the context of discussion here, theamplitude A of the shock wave is directly proportional to the stress Sand each heel strike with the ground constitutes one cycle of loading.An average person makes approximately 10⁶ heel strikes per year on eachfoot. This is based on about 3 miles of impact running each day thatcould arise from simple running, climbing stairs, or spot running suchas while performing aerobic exercises in a gym. The value of S at thejoints during normal walking has been estimated between 1.5 and 3 MN/m²,which will correspond to A values of about 0.4 to 0.6 G. Magnitudes ofboth S and A increase during running, with the specific value dependingupon the speed of the run. Since S and A are proportional, the factor bywhich S will increase will be roughly the same amount as the increase inthe G-force (or A) measured in our experiments during running. Thisfactor is about 3 to 5 times higher as seen in Table 2 of FIG. 9B andTable 3 of FIG. 9C. For example, for Shoe A data shown in Table 2 ofFIG. 9B, the G force measured during a 9.4 mph run is 3G which is about5 times the G force measured during walking of 0.6G. Similarly Table 3of FIG. 9C shows that a professional athlete running at 9.4 mph withShoe B experiences a 2.5G force which is about 4 times 0.6G that heexperienced during walking with the same shoes. Embodiments of theclaimed invention were able to reduce the G force (or S) anywherebetween 20% and 30%.

So the natural question to ask is how much increase in the cartilagelife (which directly controls osteoarthritis) one can expect if theimpact force level is reduced by 20% to 30% as accomplished by theclaimed invention? If this is significant, it could make the value ofthe claimed invention quite significant. In the following, calculationsare made for different running speeds. For each running speed, thebeneficial effect for runners of different age group is also determined.First consider a running speed of 6.3 mph. This corresponds to a valueof S equal to about 7 MN/m.² Based on equation (1), at this level of S,the cartilage life is about 38 years, 17.4 yrs, 3 years, and 0.9 yearfor population with 30 years, 40 years, 50 years and 60 years of age,respectively, assuming an individual makes 10⁶ foot-impacts each year,which as discussed above will correspond to an individual walking (stairclimbing) or running (including spot running during aerobic exercising)about 2.6 miles/day. Now let us calculate the increased life of thecartilage for various age groups, if S or A is decreased by 20%, aspossible with the claimed invention. For a 30-year-old person who runsat the 10⁶ foot-impacts per year level, a 20% reduction in A (and hencein S) will result in an astonishing 5 times (500%) increase in thenumber of cycles to failure for a 30 yr old population. This willroughly correspond to 60 years of increased cartilage life. Similarcalculations yield, on an average, an enhancement of 17.4 years for 40yr old, and 4.9 years for 50 yr old population. Thus, any technologythat can reduce the stress S or impact amplitude A by 20% could bereally significant for population with age exceeding 40 years of age. A30% decrease in S will further enhance the life of the cartilage. For 50years olds, this could add 13.4 years, while for 60 years olds this willincrease the cartilage life by 3.8 years. All the above estimations arefor level of stress in the joints that will probably be caused in apopulation that is involved with moderate exercising. The same set ofcalculations can also be done for lower level of physical activity, sayone that places the stress in the joint to about 6 MN/m.² A 10% decreasewill enhance the cartilage life by 14.3 years; 4 years, and 1 year forthe 40 years, 50 years, and 60 years old population. A 30% decrease willenhance it by 110 years, 31 years, and 8.8 years, respectively. Itappears that if one is able to reduce S or G-force by 30% it can almostavoid osteoarthritis in a healthy population with age 40 years andhigher. It certainly will provide significant relief to population thatalready suffers from arthritis. Any technology that can reduce the peakshock wave amplitudes should benefit the current elderly population andfuture population of baby boomers.

So far in this application novel designs have been discussed to reducethe G-forces that are subjected on a runner's body. There are situationsin many sports such as basketball and racquet sports (tennis, squash,etc.) where the athlete is required to make quick and abrupt changes tohis body, which inadvertently places very large pressures on discreteportions of the shoe's outer sole 12 and inner sole 15 about which thebody is being pivoted. Under such increased pressure, the said soleareas compress more that other sole areas, the result of which is notonly to provide a decreased support from the shoe but also to increasethe ground contact time for the body, which in turn can slow down theathlete's movements. This can be important for professional players.Excessive displacement of the sole also makes the athlete prone to theinjuries especially when such pivoting actions are quick with the bodybeing aggressively jostled about the pivot point.

Because of the above reasons, it is desirable to have a sole material(both for outer sole 12 and inner sole 15 for shoes and removable soles65 and 75) that would respond to the high pressure from the body byactively increasing its own stiffness. This way the sole will provideincreased resistance to areas of the athlete foot about which theathlete is pivoting. This will also result in a smaller soledisplacement and consequently lowering the ground contact time for thebody during the pivoting action. Sophisticated electronic sensors andactuator-based shoe soles have been designed that essentially work likethe car suspension systems. These are very expensive and therefore notaccessible to general population. Additionally the effectiveness ofthese active systems is limited by how densely these sensors andactuators can be placed throughout the shoe's sole.

An alternate idea, claimed here, is to accomplish the above goals usinga passive system without using the sophisticated sensors and actuators.In one embodiment of the claimed invention the sole material comprises atwo-phase substance designed to change its stiffness when subjected tohigher pressures by undergoing transformation in its internal materialstructure. In other words in this embodiment as the pressure isincreased that area of the sole material will undergo transformation inits material structure to increase its stiffness while the rest of thesole will naturally deform. In other specific embodiments of the claimedinvention the sole material 12 or 15 or 65 or 75 comprises a rubbermatrix and/or filler having a phase transformation property such thatthe substance 40 can be reversibly transformed to a crystal structureunder increased pressure to thereby have a higher stiffness thancompared with its natural crystal state. Examples of fillers, which arenot meant to be exhaustive, include active materials such as ninitol. Inanother embodiment of the claimed invention, the sole material comprisesa single-phase material that is capable of undergoing a phasetransformation allowing for enhanced stiffness with the displacement ofthis substance remaining essentially constant under increasing pressure.In one embodiment of the claimed invention, the sole material has anegative Poisson's ratio such that when the sole is compressed by thepressure from the foot the sole material contracts in its planeperpendicular to the direction of the applied foot pressure. The aboveembodiment can be utilized for example in walking shoes for heavierpersons, for whom the sole displacements are excessive, resulting inuncomfortable walking experience and increased wear rates of the sole.

The basic underlying concept leading to the above embodiments can alsobe extended to other product lines. For example, it could be utilized inmats that can be used by individuals engaged in aerobic exercises thatrequire jogging or stepping on the same spot. For these applications,mats can be provided with cavities on their outer surface.

Additional modifications and improvements of the present invention mayalso be apparent to those of ordinary skill in the art. Thus, theparticular combination of parts described and illustrated herein isintended to represent only certain embodiments of the present invention,and is not intended to serve as limitations of alternative deviceswithin the spirit and scope of the invention.

1. Footwear for reducing contact forces, comprising: an outsole unithaving an outsole upper side; and an insole unit having an insole lowerside secured to the outsole upper side and an insole upper sidecomprising a cavity wherein the cavity is adapted to receive a portionof an individual's heel.
 2. The footwear of claim 1 wherein the insoleunit and outsole unit are configured as a unitary structure.
 3. Thefootwear of claim 1, wherein the cavity is configured to contain aliquid.
 4. The footwear of claim 3, wherein the liquid is configured tosupport a portion of an individual's heel.
 5. The footwear of claim 1,wherein the cavity is configured to contain a solid.
 6. The footwear ofclaim 5, wherein the solid is configured to support a portion of anindividual's heel.
 7. The footwear of claim 1, wherein the cavitycontains a first layer and a second layer wherein the first layer isdisposed above the second layer and the stiffness of the first layer andthe second layer differ.
 8. The footwear of claim 1, wherein the cavitycontains means for supporting a portion of an individual's heel.
 9. Afootwear insert for reducing contact forces, comprising: an insole unitadapted to be inserted into footwear wherein the insole comprises acavity adapted to receive an individual's heel.
 10. The footwear insertof claim 9, wherein the cavity is configured to contain a liquid. 11.The footwear insert of claim 9, wherein the liquid is configured tosupport a portion of an individual's heel.
 12. The footwear insert ofclaim 9, wherein the cavity is configured to contain a solid.
 13. Thefootwear insert of claim 12, wherein the solid is configured to supporta portion of an individual's heel.
 14. The footwear insert of claim 9,wherein the cavity contains a first layer and a second layer wherein thefirst layer is disposed above the second layer and the stiffness of thefirst layer and the second layer differ.
 15. The footwear insert ofclaim 9, wherein the cavity contains means for supporting a portion ofan individual's heel.
 16. A sock for reducing contact forces, comprisingan insole unit wherein the insole unit comprises a cavity adapted toreceive an individual's heel.
 17. The sock of claim 16, wherein thecavity is configured to contain a liquid.
 18. The sock of claim 16,wherein the cavity is configured to contain a solid.
 19. The sock ofclaim 16, wherein the cavity contains a first layer and a second layerwherein the first layer is disposed above the second layer and thestiffness of the first layer and the second layer differ.
 20. The sockof claim 19, wherein the32cavity contains means for supporting a portionof an individual's heel.